From: lkcl <lkcl@web>
Date: Sat, 13 Feb 2021 21:24:36 +0000 (+0000)
Subject: (no commit message)
X-Git-Tag: convert-csv-opcode-to-binary~184
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=8efad93794277a20d89c56be731bf3e3ad6d4d4b;p=libreriscv.git

---

diff --git a/openpower/sv/bitmanip.mdwn b/openpower/sv/bitmanip.mdwn
index 19b4a528b..057cf2bb8 100644
--- a/openpower/sv/bitmanip.mdwn
+++ b/openpower/sv/bitmanip.mdwn
@@ -278,12 +278,21 @@ uint_xlen_t bmext(RA, RB, sh)
 }
 ```
 
-bitmask extract with reverse
+bitmask extract with reverse.  can be done by bitinverting all of RA and getting bits of RA from the opposite end.
 
 ```
 msb = rb[5:0];
 rev[0:msb] = ra[msb:0];
 rt = ZE(rev[msb:0]);
+
+uint_xlen_t bmextrev(RA, RB, sh)
+{
+    int shamt = (RB & (XLEN - 1));
+    shamt = (XLEN-1)-shamt;  # shift other end
+    bra = bitreverse(RA)     # swap LSB-MSB
+    mask = (2<<sh)-1;
+    return mask & (bra >> shamt);
+}
 ```
 
 | 0.5|6.10|11.15|16.20|21.26| 27..30  |31| name   |